Purification of water becomes more and more important due to contaminations obtained in ground water reservoirs, so called as natural aquifers.
Commonly, purification of water takes place by having water primarily reacted with different oxidation agents, then having it penetrated through specially arranged layers of gravel, sand and other materials, and then transporting the water thus purified via a pipeline system, optionally provided with pressure increasing pumping stations and/or water towers, to the consumer.
Ground water and raw water, which are used for drinking or tap water production often contain high amounts of iron, manganese, arsenic, fluoride and other trace elements. High levels of above mentioned trace elements have to be reduced before the water can be used for tap water (drinking purpose) due to health and taste reasons. EP-A-0 160 774 describes the use of a zone for oxidation and precipitation of iron and manganese where water containing oxygen or oxygen producing compounds intermittent are added to the zone via satellite wells arranged around extraction wells. Hereby water is fed only to a few satellite wells and simultaneously water is extracted from adjacently situated satellite wells. The water enriched with oxygen and free of any air bubbles is forced down the satellite wells. The addition of dissolved Oxygen creates a suitable growth environment for microorganisms present in the ground, which microorganisms together with chemical and/or biochemical processes provide for precipitation of iron and manganese in the zone/ground layer, which will serve as a reactive filter for the removal of arsenic, fluoride and other trace elements. Iron oxidizing bacteria assists in the oxidation of ferrous iron of the untreated water. This action is repeated at specific intervals to obtain pure water. However, it is not only iron and manganese that are a problem but other metals, metalloids, nitrate, nitrite, pesticides and organic sourced micro contaminants need to be eliminated to produce a healthy water, particularly when considering tap water quality.
In earlier patent (U.S. Pat. No. 475,304) another method to improve the above process was used, which included working with three so called mainwells which were placed with linear distances of 600 meter to 1000 meter from each well. Groundwater was pumped up from one well and part of this water was enriched with oxygen and recharghed into the other two wells. The circular arrangement of oxygenated water around the recharghed wells allowed to withdraw a limited amount of purified water before again a recharge had to occur. This system showed several disadvantages in the operation, energy consumption and removing of other trace elements than Iron. Further on this was not an artificial aquifer but was built in the natural aquifer.
EP-A-0 154 105 describes reduction of nitrate in ground water by means of denitrification in a reduction zone created between injection/satellite wells also arranged around one or more extraction wells.
According to the method and system as disclosed in EP-A-0 154 105, a different method of creating oxidation and reduction zones was perceived, and achieved. An oxygen enrichment system is placed above ground in the satellite wells to cover, thus oxygenating the pumped up water before flowing back into the satellite wells. In these wells a separator was present in each well which divided the well into an upper and a lower part Inflow of compressed air is achieved through a first pipe into the upper half of the well, and through a second pipe into the lower half of the well. Water may be pumped from the upper half of the well for a certain time duration after which it may be pumped from the lower half of the well for the remaining time duration. In the disclosure the feeding of water is restricted to some wells to create a denitrification zone. Thereby all the aquifer is not used for denitrification purpose.
It is previously known to create reaction zones in aquifers to obtain an oxidation and a precipitation zone or a reduction zone between a number of injection or satellite wells arranged around one or more extraction wells in such reaction zones, whereby the zone desired is created intermittently or continuously between each pair of adjacent situated injection wells by introducing oxygen, oxygen containing gas or oxygen releasing compounds in the water of the two injection wells when one creates an oxidation and precipitation zone, or introduce an oxygen consuming compound in the injection wells to obtain a reduction zone, and whereby one pumps the water of one of the satellite wells into the neighbouring satellite well so that a circulation circuit is created in the aquifer between the two satellite wells.
However, in certain areas of the globe the natural layers have been destroyed by contaminants or there is a lack of natural uniform layers with suitable material compositions. For that reason artificial aquifers have been proposed, whereby the artificial aquifer consists of a basin, normally covered with an impermeable cloth or sheet to provide a defined volume. The basin is then filled with gravel and sand, and is provided with tubings and wells to a) add ground water or any other raw water to the basin, b) create the demanded reactive zone for the precipitation and c) to remove the water having been treated in the basin.
The present invention is based on the known in situ process with the name Vyredox or Nitredox. The artificially built plant will be operated under the same conditions as created in the natural in situ plants. The bottom of the present plant is tightened up with a impermeable membrane to isolate the plant from the natural ground aquifer and to provide for the possibility to use special natural derived washed or unwashed filling materials to create ideal conditions for the spread out of the activated reactive zone as quick as possible as well as to maintain the appropriate flow and hydrological conditions.
EP 1 436 469 related to a certain construction of satellite well pipes, also discloses the use of artificial aquifers, wherein the supply tubing is placed midway down in the reaction zone of gravel and sand
To overcome the problems arising due to clogging of toe earlier embodiments, system as discussed in patent EP 1 436 469 and method was derived. Pressure inlet pipes were introduced in the upper half as well as the lower half of the wells. The upper half and lower half were defined by introduction of a balloon body which acted as a separator. Conduits supported the pressure inlet pipes, in each half. A circulation vessel was provided, above the ground, over each well. Initially, air/water was supplied to the upper half of the well and water was pumped upwardly into the circulation vessel for being de-aerated. The water flowed then by gravity into the lower half of the well, below the balloon body. This procedure was carried out for a certain time duration in one or more satellite wells. In another satellite well, or for the remaining time duration, air was pressurized into the lower half of the well, below the balloon body. The upflow of water was directed into the aeration and de-bubbling vessel. This de-bubbled water flows back into the top half of the well, before it passes out of through the well screen, into the ground.
WO 2006/014126 discloses another artificial aquifer working under a negative pressure and therefore using a complete water and air tight enclosure. Also in this case the supply tubing is placed midway down in the aquifer and the satellite wells are special designed.
Further enhancements in WO 2006/014126 patent application, included placing a plurality of satellite wells in a circular or rectangular way, as well as one extraction well in their centre. The infiltration system was arranged close to the satellite wells. An oxygen enrichment system was placed above ground. These wells and infiltration system were placed in artificial aquifers developed by placing filter material to define a manmade basin of the aquifer, beneath the ground. There was a need to hermetically seal all these wells and all covering. Due to this specific assembly, dead zones were created at the sides of the artificial aquifer. The deadzones were created due to non-circulation of water in those zones. In its typical working, water entered the satellite wells through its permeable screens, before being directed out to the oxygen enrichment system. Oxygenated water re-enters the satellite wells and therefore the whole of the aquifer. The main flow of water is thus established, that purified water enters the extraction well, in the centre, and can be pumped out, for use. The hermetic sealing of the aquifer is needed for the proposed operation under negative pressure. The inhomogeneity between the activated zones and the dead zones provides severe issues. Working under negative pressure is very energy consuming and requires a very high technological sealing to be acquired. Thus it is high energy and cost requiring.
Thus in these known constructions, dead zones will be created, in particular over the supply tubing, which dead zones will disturb the activity in the reaction zone, as the environmental differences between the dead zones and the reaction zone are too great.
A further problem solved is to maintain the growth environment of the microorganisms carrying out the purification of the water in the aquifer. Thus the aquifer may not be dried out, i.e., emptied completely, changing the hydrology around the microorganisms.